1. Field of the Invention
The present invention relates to lamination of films formed in many layers on a substrate such as, for example, a substrate with an oxide surface.
2. Description of the Prior Art
Up to the present, many attempts have been made to form a film of carbon or a film in which carbon is the main component, which are hereinafter referred to as a carbon-type film, on various types of substrates. However, some substrates have poor interface characteristics, in particular the adhesion characteristics, with some carbon-type films. Cracking and peeling often occur, and the advantages of the carbon-type film, for example, resistance to wear, high degree of smoothness, high hardness, and the like, have not been adequately attained.
When a conventional carbon-type film is formed directly on a substrate, if the film is thin, there is often no problem with adhesion, but if the film is thick, there is a high possibility of cracking and peeling.
For example, when a carbon-type film formed on a substrate at 350.degree. C. or greater is left at a room temperature, the carbon-type film will eventually drop off or peel away. Also, when a carbon-type film formed at a room temperature is subjected to the heat treatment at a high temperature such as 400.degree. C. or greater, specks of the film peel away or the film falls off.
The film in the former case is generally said to be subject to thermal stress, which is produced because of the difference between the thermal expansion coefficient (or thermal contraction coefficient) of the film itself and that of the substrate. In the latter case, the effect of stress relief by hydrogen is reduced because of the decrease in C-H bonds (hydrogen contents) throughout the film.
Many attempts have been made to deposit carbon coatings on a surface of various types of substrates; however, when a substrate is made of an oxide material, C-0 bonds tend to be formed at an interface between the oxide material and the carbon coating. As a result, the reliability of the coating for example, the adhesivity of the coating to the substrate is degraded. On the other hand, it has been known to interpose a buffer layer such as a silicon nitride layer at the interface between the substrate and the carbon coating; however, sufficient results have not been obtained.
In accordance with the present invention, it has been recognized that the physical properties of the laminate member composed of the carbon layer and the silicon nitride layer formed on the oxide substrate are largely influenced by a hydrogen concentration in the silicon nitride layer.